The Ocean is Slowly Adapting to Climate Change, But at What Cost?

Observing twenty generations of whales or sharks as they adjust to climate change, tracking their evolution and biology as temperatures and carbon dioxide levels rise. This could reveal a lot about how resilient life in the oceans is to climate change. However, it would take hundreds of years, which is inconvenient for scientists and politicians attempting to comprehend our rapidly warming planet.

Consider the life of the copepod Acartia tonsa, a minor and insignificant water organism on the bottom of the food chain. It reproduces, develops, and generates a new generation in around twenty days. In roughly a year, twenty copepod generations pass.

An Intrinsic Study

A team of six scientists, led by University of Vermont (UVM) biologist Melissa Pespeni and postdoctoral scientist Reid Brennan, did just that: In a first-of-its-kind laboratory experiment, they exposed thousands of copepods to the high temperatures and high carbon dioxide levels that are predicted for the future of the oceans. And watched as twenty generations passed.

They then removed some of the copepods and returned them to the baseline circumstances, similar to today's ocean conditions in terms of temperature and CO2. And then they kept watching as three more generations passed.

The findings, which were published in the journal Nature Communications, "suggest that there is hope, but also complexity in how life adapts to climate change," according to Pespeni.

Her optimism stems from the team's observation that the copepods did not perish due to climate change. Instead, they endured and even flourished. Many changes in the copepods' genes related to how they manage heat stress, grow their skeletons in more acidic waters, produce energy, and other cellular processes affected by climate change were recorded by the scientists from UVM, University of Connecticut, GEOMAR Helmholtz Center for Ocean Research in Germany, and the University of Colorado, Boulder.

This shows that these creatures have the capacity in their genetic makeup-using the variation in natural populations-to adapt over twenty generations, evolving to maintain their fitness in a radically changed environment.

According to the team, copepods-a worldwide dispersed group of crustaceans consumed by many economically significant fish species-could be robust to the unusually fast heat and acidification currently being released in the oceans by humans' fossil-fuel consumption findings.

Critical Observation

The team's observation of what occurred to copepods restored to baseline settings led to the complexity-"it's a caution, really," Pespeni adds. These organisms showed the hidden cost of the prior twenty generations of adaption.

When the copepods sought to return to what had previously been benign settings, the flexibility that had helped them evolve over twenty generations-what scientists call "phenotypic plasticity"-was destroyed. Copepods brought "home" were less healthy and formed smaller populations.

They were able to re-evolve back to their ancestral circumstances after three generations. Still, they had lost the capacity to endure a low food supply and exhibited diminished tolerance to new types of stress.

Becoming Wary of Oversimplified Models

Reid Brennan, who completed this study in Melissa Pespeni's lab at the University of Vermont and is now at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, cautioned against overly simple models that look at just one variable when predicting how well species will do and which ones will survive into the future.

The scientists' latest research of copepods also hints at a bigger fact about evolution's complicated economy: there may be unintended consequences to rapidly growing in a suddenly heated world.

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